Breast cancer is a heterogeneous disease comprised of at least 5 major tumor subtypes that coalesce as the 2nd leading cause of cancer death in women in the United States. Amongst individual breast cancer subtypes, those classified as being triple-negative breast cancers (TNBCs) are clinically unique via their presentation of aggressive and metastatic phenotypes, and their high propensity to recur rapidly following conventional chemotherapy treatment. TNBCs are also noteworthy by their failure to express hormone receptors (estrogen and progesterone) and ErbB2/HER2, a phenotype that renders targeted chemotherapies (e.g., hormonal or HER2-directed) ineffective and contributes to the poor prognosis of TNBC patients. Although our understanding of the molecular features and clinical manifestations of TNBCs has increased in recent years, science and medicine still lack sufficient knowledge of TNBC development and metastasis to permit the synthesis of chemotherapies capable of specifically targeting and alleviating this aggressive breast cancer subtype. c-Abl is a ubiquitously expressed nonreceptor protein tyrosine kinase that governs cell proliferation, migration, and adhesion, as well as that of cell survival. Additionally, c-Abl can function as a suppressor or promoter of tumorigenesis in a cell- and context-specific manner. Importantly, we showed that the enforced expression of a constitutively-active c-Abl mutant (CST-Abl) alleviated TNBC development and metastasis in mice, doing so by inducing TNBCs to undergo mesenchymal-epithelial transition programs coupled to elevated p21 expression, and to diminished expression of matrix metalloproteinases. Along these lines, we recently observed TNBC tumorigenicity to be inversely related to c-Abl expression levels, which also predicts for TNBC response to docetaxel. Likewise, we discovered that the ancient Chinese herb Securinine exhibits potent cytotoxic activity against TNBCs propagated in 3D-organotypic cultures. Based on these and other preliminary findings, we hypothesize that measures capable of promoting c-Abl expression and activation will alleviate TNBC development and metastatic progression. These hypotheses will be addressed by four Specific Aims. Aim 1 will determine the role for oncogenic TGF-? signaling and mechanotransduction to inactivate the tumor suppressing functions of c-Abl in TNBCs. We will manipulate, both positively and negatively, the expression of ?1 and ?3 integrins and their effectors to gauge their function in driving c-Abl inactivation during specific stages of TNBC development and metastatic progression. Likewise, the validity of these molecular changes will be assessed using a human breast tissue microarray. Aim 2 will determine the role for p53 members in mediating tumor suppression by c-Abl in TNBCs, and in other non-TNBC subtypes. Additionally, the effectiveness of a novel allosteric c-Abl activator, DPH, to eradicate TNBCs will be assessed using in vitro and in vivo models of TNBC tumor development. Aim 3 will determine the value of c-Abl to predict TNBC response to docetaxel. We will manipulate c-Abl expression in human and murine TNBC cell lines, whose survival following docetaxel treatment will be assessed both in vitro and in vivo. Likewise, we will perform a retrospective study on annotated clinical specimens to validate c-Abl expression as a predictive biomarker for TNBC response to docetaxel. Lastly, Aim 4 will determine the therapeutic effectiveness of Securinine to eradicate TNBCs. Here we will manipulate the expression of c-Abl and p53 family members in late-stage TNBCs, whose survival when treated with Securinine, docetaxel, and TNBC standard-of-care agents will be determined and compared. Collectively, the findings obtained in this innovation application will provide novel molecular insights into how c-Abl suppresses TNBC tumorigenicity; they will also generate innovative translational outcomes in the form of novel biomarkers (e.g., c-Abl for docetaxel response) and treatment options (e.g., Securinine and DPH) for TNBCs.